JPH0343535B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a gas turbine combustor having a two-stage combustion structure, and particularly when using gaseous fuel such as natural gas (LNG), there is a significant
This invention relates to a gas turbine combustor that can reduce NOx.

[Background of the invention]

First, of the generally known conventional combustors aiming at low NOx, the technology closest to the present invention will be explained. A combustor that adopts a two-stage combustion method is, for example, as shown in Japanese Patent Application Laid-Open No. 57-41524,
Fuel and air are introduced into the first stage (head) combustion chamber to perform diffusion combustion using a single nozzle, and fuel and air are introduced into the second stage combustion chamber (rear) on the wake side (downstream in the flow direction of combustion gas). This system aims to reduce NOx by supplying a mixed gas of 100 to 1000 ml and performing low-temperature combustion due to excess air as a whole.

However, the method of forming a diffuse combustion flame in the head combustion chamber with a single nozzle and injecting the second stage fuel from its wake has the drawback that NOx cannot be significantly reduced. This is because, although the generation of NOx in the second stage combustion can be suppressed when fuel is introduced in the second stage, the formation of hot spots with high temperatures over a wide range occurs during the diffusion combustion in the first stage, resulting in the generation of NOx. cannot be suppressed. Furthermore, in the case of a single nozzle, since the nozzle is located at the axial center of the combustion chamber, the air flow supplied from the side wall of the combustion chamber and the fuel supplied from the nozzle are not mixed well, which causes the existence of hot spots. As described above, the conventional combustor equipped with a single fuel injection nozzle in the head combustion chamber has the disadvantage that it cannot significantly reduce NOx. In order to significantly reduce NOx even in a two-stage combustor, it is necessary to
It is necessary to suppress NOx.

[Purpose of the invention]

The present invention has been developed with this in mind, and its purpose is to suppress the production of NOx through low-temperature lean combustion in both the head and rear parts, and to achieve a significant reduction in NOx. To provide a turbine combustor.

[Summary of the invention]

That is, the present invention provides a gas turbine combustor in which diffusion combustion is performed in the head combustion chamber and premix combustion is performed in the rear combustion chamber. A plurality of premixed gas supply ports are arranged at the head of the head combustion chamber, and a premixed gas supply port for supplying second stage fuel at the rear is arranged near the peripheral wall of the rear combustion chamber, and a premixed gas supply port is arranged near the peripheral wall of the head combustion chamber, and , the upstream end is located at the head end of the head combustion chamber,
The intended purpose is achieved by providing an inner cylinder whose downstream end is located downstream of the combustion jet port of the first stage fuel supply nozzle and upstream of the premixed gas supply port. It is something.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described using FIG. 1.

The gas turbine is composed of a compressor 1, a turbine 2, and a combustor 3, and the combustor 3 includes a combustion tube 4,
It consists of an outer cylinder 5 and a transition pipe 8 that guides combustion gas 7 to the turbine stationary blades 6, and a first stage fuel nozzle body 9 is provided at the closed end on the head side of the outer cylinder 5. . Note that 10 is a cover to which this fuel nozzle body is attached. In addition, although not shown, the combustor is equipped with a spark plug for ignition, a flame detector for detecting flame, and the like. The combustion tube 4 is divided into a head combustion chamber 11 and a rear combustion chamber 12 with a larger diameter.
That is, the inner cylinder 13 is inserted into the shaft center.
The inner cylinder preferably has a cone shape that tapers toward the downstream side.

The solid line arrows in the figure indicate the air flow, and the compressor 1
The airflow 14 compressed by
The air is introduced into the respective combustion chambers through the second-stage air passage 32 for combustion, the combustion air holes 19 and the cooling air holes 20 opened in the head combustion chamber, and the like.

The first stage fuel nozzle 22 attached to the cover 10 is connected to the head combustion chamber side wall (liner cap) 21.
A plurality of cylinders are installed coaxially with the axis of the combustor to inject fuel into the head combustion chamber. 27 in the figure
is the fuel outlet of the nozzle.

The inner cylinder 13 is provided with an air inlet hole 23 for introducing air, and the surface of the inner cylinder 13 is provided with a plurality of cooling air holes 24 in a plurality of rows so that cooling air flows along the surface. There is.

Further, FIG. 2 shows the detailed structure of the combustor.

Combustion occurs in the head combustion chamber 11 as follows. That is, a plurality of first stage fuel supply nozzles 22 are provided upstream of the head combustion chamber 11 by penetrating the liner cap 21.
The fuel 26 ejected from the first-stage fuel supply nozzle passes through the opening in the liner cap 21 and between the nozzle and the air 28 from 29 and the air hole 19a opened in the wall of the head combustion chamber. ,19b,1
It mixes with air from 9c and 19d and combustion progresses.

The first-stage fuel supply nozzle 22 is different from the arrangement of a single injection nozzle in the prior art, and is located close to the side wall of the head combustion chamber. ,19b,
19c and 19d and the air stream 28 are quickly mixed, so that the cooling effect of the air can be increased at the beginning of the combustion process. Therefore, the occurrence of hot spots is suppressed,
It is possible to reduce NOx.

Furthermore, by performing a plurality of fuel injections, it is possible to disperse the flame, and due to the mutual effect of these, it is possible to achieve low NOx. The trapezoidal cone-shaped inner cylinder 13 provided in the center of the head combustion chamber promotes mixing of fuel and air. That is, air holes 19a, 19b, 19c, 19 opened in the side wall of the head combustion chamber as seen in the prior art.
The phenomenon in which the cooling mixing effect is reduced due to the air from d not reaching the center is eliminated.
Further, since the flame is effectively cooled from the inside by the cooling by the inner cylinder itself and the cooling air 24 jetted from the surface of the inner cylinder 13, a significant reduction in NOx can be achieved. Furthermore, the length of the first-stage fuel injection port 27 protruding into the combustion chamber affects the mixing with the air flowing in from the upstream side of the fuel injection port 27, so the injection port is located as close to the air hole 19 as possible.
It is desirable to locate it near a and 19d. In other words, it is desirable that it protrude from the liner cap.

Next, the positional relationship between the inner cylinder 13, the head combustion chamber 11, and the premixed gas supply port for supplying the second stage fuel will be explained together with the method of operating the present combustor.

As is well known, a gas turbine with a two-stage combustor of this type operates only by combustion in the head combustion chamber from startup to light load, and during high load operation, combustion occurs in the head combustion chamber and combustion occurs only in the head combustion chamber. It is operated by both combustion in the rear combustion chamber. Therefore, the relationship between the length of the head combustion chamber and the second stage fuel supply position is determined by considering the following effects including the inner cylinder located within the head combustion chamber. That is, combustion of the first stage fuel is almost completely completed in the annular space 25 in the head combustion chamber 11, and even if the second stage fuel and air are supplied and combusted, the head combustion chamber 11 The aim is to suppress fluctuations in the internal flow and changes in the amount of incoming air to the minimum. In order to achieve this effect, the first stage fuel 26 mixes with the incoming air 19a to 19d and the air 28 in the annular space 25 surrounded by the inner cylinder 13 and the inner wall of the head combustion chamber, and almost It is necessary to define the head combustion chamber 11 in such a way that complete combustion occurs.

FIG. 4 schematically shows the formation of the first stage flame 45 in the head combustion chamber. If the length of the head combustion chamber 11 is shortened, the fuel and air flow from the second stage will be introduced before combustion in the head combustion chamber 11 is completed, resulting in the following phenomenon. In other words, in the case of only head combustion, the first stage flame 45 extends to the rear combustion chamber, but the progress of combustion is blocked by the air from the second stage, and the part indicated by A is rapidly cooled, so CO and It has the disadvantage that unburned components such as HC are produced in large quantities, reducing combustion efficiency. Also, if the second stage combustion is performed in such a structure, the first stage combustion and the second stage combustion will proceed at the same time, resulting in a high temperature hot spot at the beginning of the second stage combustion.
It has the disadvantage of generating more NOx. Furthermore, as the length of the head combustion chamber increases, the cooling area of the wall of the head combustion chamber increases. Therefore, the amount of cooling air increases. By increasing the amount of cooling air in this way, cooling air is introduced between the first stage flame and the second stage fuel gas when the second stage is introduced, so the first stage fuel gas is transferred to the second stage fuel gas. The length of the head combustion chamber cannot be made longer than necessary because the flame transfer properties will be poor. According to tests conducted at a combustion pressure of 10ata and an air temperature of up to 350°C, the length of the head combustion chamber is also controlled by the diameter and length of the inner cylinder 13, but typically the length of the head combustion chamber 11 is determined by the outer diameter of the head combustion chamber 11. It is desirable that it is about 1.2 to 2.0 times, and the best is about 1.5. On the other hand, the length of the inner cylinder 13 is also related to the volume of the head combustion chamber 11, but basically, if it is longer than the head combustion chamber 11, when the second stage combustion starts, the rear combustion chamber The gas flow velocity increases due to combustion gas expansion that occurs within the combustion chamber, but this rate of increase increases by the decrease in flow path area due to the protrusion of the inner cylinder, and the flow resistance at the outlet of the head combustion chamber, which changes as the square of the gas flow velocity, increases. growing. Therefore, during the second stage combustion, the flow rate of air introduced from the head combustion chamber 11 decreases, and low temperature combustion due to excess air becomes impossible in the head combustion chamber 11.
NOx generation increases. Furthermore, since the gas temperature increases and the air flow rate decreases, the temperature of the outer circumferential wall of the head combustion chamber 11 increases, which shortens the reliability and life of the combustor. Therefore, it is necessary to determine the length of the inner cylinder 13 so as to minimize the influence of flow resistance caused by second-stage combustion. For this purpose, the length of the inner cylinder 13 is made shorter than the head combustion chamber 11, and the flow area of the combustion gas is made large from the tip of the inner cylinder to the outlet of the head combustion chamber to prevent rapid expansion of the combustion gas. It is necessary to take up a volume that can withstand it. In experiments, the best ratio of the length l of the inner cylinder 13 to the length L of the head combustion chamber 11 is l/L = 0.7, and based on this dimensional relationship, from the tip of the inner cylinder,
It is best to provide enough space to the rear end of the head combustion chamber. Here, when l/L is small, that is, when the inner cylinder is shortened, the first stage combustion flame is formed at the axial center of the tip of the inner cylinder, and a high temperature part is formed at the axial center, so NOx Occurrence increases.

In the same combustion test as mentioned above, NOx in the 1st and 2nd stage
The air opening area of each part that can reduce CO and HC and provides good combustion characteristics with less CO and HC generation is as follows when expressed as a percentage (%) of the total opening area.

(1) Opening area of head combustion chamber (19, 20, 28)
Percentage: 50-55%.

(2) Second stage (rear) combustion air hole area (32) ratio: 20-30%.

(3) Rear combustion chamber opening area (16, 18) ratio:
10-30%.

(4) Opening area of inner cylinder cone (24) ratio: 5 to 10
%.

In particular, when combustion air holes are opened in the inner cylinder in addition to cooling air, combustion is promoted by this air flow, resulting in the formation of hot spots and heating of the vicinity of the air holes. Therefore, it is desirable that the inner cylinder has a structure in which only the cooling air holes are opened. Furthermore, if the air area to the second stage is increased to 30% or more, there is a drawback that the flame transfer performance decreases, and if it is less than 20%, the NOx reduction effect becomes small.
On the other hand, if the amount of air to the head combustion chamber 11 exceeds 60%, the mixed gas will become diluted and more CO and HC will be produced, while if it is less than 40%, NOx will be generated and the metal temperature will rise.

Next, the second stage combustion will be explained using FIGS. 5 to 7. The fuel 17 passes through a path portion 30 (FIG. 7), is guided to a fuel tank 31, and from there is deposited near an air hole 33 (FIG. 5) that opens into a second stage air passage 32 and a rear combustion chamber 12. supply. This fuel supply is performed from the fuel injection holes 35 of the plurality of fuel nozzles 34 along with the air flow of the air holes 33. The second stage air flow 36 is preferably supplied as a swirling flow so as to lengthen the combustion time as much as possible when being supplied to the rear combustion chamber.
Therefore, the air passages are partitioned by a plurality of rotating vanes 37, and each air passage has a fuel injection outlet 3.
5 is opened to promote mixing of air and fuel, and the excess air is supplied to the rear combustion chamber as a mixed gas 38, which is ignited from the flame in the head combustion chamber to perform low-temperature dilution combustion.
Aim to reduce NOx. In the second stage combustion
The key to reducing NOx is how well the air and fuel are mixed, and for this purpose it is better to make the mixing time as long as possible. For this reason, by providing the swirling vanes 37, the mixing time can be increased by the length of the flow path, and the uniformity of the mixing can therefore be improved. On the other hand, what is important for second-stage combustion is not to draw flame into the second-stage air passage, especially into the swirling vanes 37. That is, the air passage surrounded by the vanes 37 is also supplied with fuel and is in a condition where it can be sufficiently combusted.
However, since the ejection speed of the air/fuel mixture passing through the vane 37 is approximately 100 m/s, and the flame propagation speed in the turbulent flow field is at most 5 m/s, under ideal conditions the flame backfires. No phenomenon occurs. However, due to deterioration in the shape and surface finish accuracy of the vane, stagnation such as a vortex is generated near the wall surface of the vane, and a so-called flashback phenomenon occurs in which the flame is drawn into the vane using the stagnation as a ignition point. As a way to deal with this, as shown in FIGS. 5 and 6, the fuel 17 is injected from the second stage fuel nozzle 34 through its nozzle 35 into an air passage surrounded by swirling vanes 37 to mix the fuel 17. It is important to aim for For this purpose, it is best to set the ejection port near the center of the swing vane, and in particular, depending on the second stage fuel supply structure, the upstream side of the swing vane 37 has a straight section along the axial direction. By using the turning vanes with curves 41a, b, c, . . . toward the downstream side, the flow of air can be made smooth, and the positioning accuracy of the fuel nozzle 34 can also be improved. Furthermore, there is no vortex or stagnation near the surface of the rotating vane 37, and no backfire phenomenon is observed, so the structure is good. In this way, the fuel nozzle 3
The position of the spout 35 opening at 4 is the rotating vane 37
By being located in the center of the air passage surrounded by air, the flow becomes smoother and the fuel is more easily dispersed almost evenly in the air passage, increasing the uniform mixing effect. Therefore, the inner cylinders 4 and 2 during combustion
It is important to ensure that the positions of the swirling vanes 37 and the fuel nozzles 35 do not shift due to the difference in thermal expansion of the outer cylinder 5 that supports the stage fuel nozzles 35, thereby reducing the uniform mixing effect. This embodiment is shown in FIG. By connecting members such as the swirling vane 37 that form the second-stage combustion air passage, especially the lower presser member 40 and the nozzle flange 39 to form an integral structure, the positions of the swirling vane 37 and the nozzle orifice 35 are always kept in the fixed position. It is something that should be maintained. Furthermore, in order to maintain the fixed position even when the gas turbine is used for a long time, the head combustion chamber 11 and the rear combustion chamber 12 each sandwich a member forming a second stage air passage, and a spring seal member 42a as shown in the figure, By connecting the combustor through 42b, the second stage air passage and the second stage fuel nozzle are freed from thermal deformation of the combustor.
On the other hand, curves 43a, 43 are formed in the air passage portion to fit the flow path so that the air flows smoothly.
The b-shape results in good uniform mixing and eliminates the formation of vortices, stagnation, etc., which is effective in preventing backfire phenomena.

On the other hand, interference between the first stage flame and the second stage flame
We will explain what influences NOx generation.
That is, as shown in FIG.
5, the first stage flame 45 and 2
In the area where the stage flame 46 interferes (indicated by 47 in the figure), a hot spot where the combustion temperature becomes high is created, so NOx is generated in large quantities. Therefore, as shown in FIG. 9, it is difficult to prevent the first stage flame 45 and second stage flame 46 from interfering with each other.
This is essential for NOx conversion, and it is a good idea to separate the flame. Therefore, the second stage flame is dotted line 48
It is also possible to form it in the direction shown by, but in this case, when the second stage fuel injection starts, the second stage combustion will be directed outward more than necessary because the performance of ignition (flame transfer) due to the head flame 45 will be reduced. It is not possible to make it form. Figure 10 shows the NOx concentration when the second stage flame is formed almost horizontally, and the NOx concentration when the second stage flame is formed at right angles.
The NOx concentration is shown as line B to compare the two. NOx can be reduced more with horizontal inflow than with right-angled inflow because there is no flame interference.

As explained above, by adopting the inner cylinder arrangement and multi-fuel nozzle in the head combustion chamber, and by supplying fuel from near the outer periphery of the combustor liner, we aim to disperse fuel and achieve uniform mixing of air and fuel. By promoting this, it is possible to achieve effective low-temperature air excess combustion and significantly reduce NOx.
In other words, as shown in Figure 11, the NOx in the first stage
Unlike the conventional technology shown by line A, when combined with the second stage shown by line B, a large reduction in NOx can be achieved.

On the other hand, the effect that the combustion state of the first stage has on the second stage will be explained using FIG. 12. 12th
The figure shows the gas temperature distribution at the outlet of the head combustion chamber. In the conventional technology in which a single fuel nozzle is installed at the axial center, the temperature at the axial center of the combustion chamber increases;
According to the present invention, the effect of fuel dispersion and the good mixing of air and fuel are achieved, so that there is no high-temperature area as seen in the prior art. Naturally, there is a tendency for some high-temperature areas to exist on the outer periphery corresponding to the flame position. In particular, in the present invention, if the inner cylinder is installed at the axial center and cooling air is supplied to the surface of the inner cylinder, there will be no high-temperature portion at the axial center. Therefore, a significant NOx reduction effect can be obtained by the first stage combustion.

〔Effect of the invention〕

As explained above, the present invention provides a plurality of first-stage fuel supply nozzles that supply first-stage fuel at the head end of the head combustion chamber and coaxially with the axis of the combustion chamber. , the premixed gas supply port for supplying the second stage fuel is arranged near the outer peripheral wall of the rear combustion chamber, and the upstream end is located near the axial center of the head combustion chamber. An inner cylinder is provided at the end, and the downstream end is located downstream of the fuel jet port of the first stage fuel supply nozzle and upstream of the premixed gas supply port. Dispersion of fuel supplied in the combustion chamber and uniform mixing of air and fuel are promoted, hot spots are eliminated, and low-temperature lean combustion suppresses NOx production in both the head and rear parts, resulting in a significant increase in NOx. It is possible to obtain a two-stage combustion type gas turbine combustor that can achieve reduction in fuel consumption.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a gas turbine combustor embodying the present invention, FIG. 2 is a partial sectional view of the combustor, and FIG.
The figure is a perspective view of the rear part of the combustor, FIG. 4 is an explanatory diagram showing the state of flame formation, FIG. 5 is a detailed view of the second stage fuel supply section, and FIG. 6 is a diagram of the second stage fuel supply section. Detailed drawings showing other embodiments, FIG. 7 is a sectional view showing other embodiments of the second stage fuel supply section, and FIGS. 8 and 9 are
Figure 10 is a diagram explaining the second stage fuel supply direction and flame interference state, respectively, and Figure 10 is a diagram explaining the direction of second stage fuel supply and the flame interference state.
Figure 11 is a characteristic diagram showing the relationship between NOx reduction effects.
FIG. 12 is a characteristic diagram showing the relationship between gas turbine load and NOx concentration, and FIG. 12 is a characteristic diagram showing the flame temperature distribution. 9...First stage fuel, 11...Head combustion chamber, 12
... Rear combustion chamber, 13 ... Inner cylinder, 17 ... Second stage fuel, 18 ... Second stage air passage section, 22 ... First stage fuel injection section, 34 ... Second stage fuel nozzle.

Claims (1)

[Scope of Claims] 1. A head combustion chamber located at the head of the combustor, into which first-stage fuel and air are introduced for combustion; and a head combustion chamber located downstream of the head combustion chamber in the flow direction of combustion gas. , a rear combustion chamber in which second-stage fuel and air are introduced and combustion is performed, and the head combustion chamber performs diffusion combustion, and the rear combustion chamber performs premix combustion. In the combustion chamber, a plurality of first-stage fuel supply nozzles for supplying the first-stage fuel are arranged at the head of the head combustion chamber, and a premixed gas supply port for supplying the second-stage fuel is arranged in the rear combustion chamber. disposed near the peripheral wall of the chamber, and located at the axial center of the head combustion chamber, with an upstream end located at the head end of the head combustion chamber, and a downstream end located from the fuel jet port of the first stage fuel supply nozzle. A gas turbine combustor comprising an inner cylinder located downstream and upstream of the premixed gas supply port. 2. The first stage fuel supply nozzle is arranged between the outer circumferential wall of the head combustion chamber and the inner cylinder, and protrudes toward the downstream side from the head end surface of the head combustion chamber. A gas turbine combustor according to claim 1. 3. The gas turbine combustor according to claim 1, wherein the inner cylinder is formed into a cone shape that tapers toward the downstream side. 4. A plurality of holes are provided in the outer circumferential wall of the inner cylinder, and a portion of the air supplied to the combustion chamber is supplied through the holes. gas turbine combustor. 5. The gas turbine combustor according to claim 1, wherein the length of the head combustion chamber along the axis is 1.2 times or more and 1.8 times or less the outer diameter of the head combustion chamber. 6. The premixed gas supply port for supplying the second stage fuel is formed so as to eject the mixed gas in a direction substantially parallel to the combustor axis. Gas turbine combustor.